Removal of carcinogenic hexavalent chromium from aqueous solutions using newly synthesized and characterized polypyrrole–titanium(IV)phosphate nanocomposite

Abstract

This paper reports the synthesis of polypyrrole–titanium(IV)phosphate (PPy–TiP) nanocomposite as a synthetic adsorbent for the adsorptive removal of Cr(VI) ions from aqueous solutions. Facile in situ chemical oxidative polymerization of pyrrole in presence of titanium(IV)phosphate (TiP) formed PPy–TiP nanocomposite. The prepared PPy–TiP nanocomposite was characterized by FT-IR, FE-SEM, TEM, EDAX and BET analysis. A strong interaction between PPy and TiP particles was observed, and the nanocomposite showed remarkable adsorption of Cr(VI) ions from aqueous solutions. In order to optimize the conditions for maximum adsorption of Cr(VI) ions, batch process was used and the effects of contact time, initial concentration, pH, point of zero charge measurement and adsorbent doses were investigated. The equilibrium isotherm data were fitted using Langmuir and Freundlich isotherms. The adsorption process based on the thermodynamic parameters was spontaneous and endothermic. Dubinin–Radushkevich (D–R) isotherm was used to calculate the mean free energy, which showed that the adsorption process involves chemical forces, hence chemical in nature. The kinetics data were evaluated using the pseudo-first-order and pseudo-second order kinetics model, and it was found that data was best fitted by the pseudo-second-order model for adsorption of Cr(VI) supporting that the adsorption mainly consisted of chemisorption. The desorption studies were also performed by batch process and ∼100% desorption of Cr(VI) ions was achieved using 0.5M NaOH solution as eluent.